4.8 2000 Silv. surging HELP!!!!!

[timber3]

I've got a 2000 Chevy Silverado 1500 4x4 with a 4.8 liter, 62000 miles. Whenever the engine is started in the cold, the rpms go up to 1500 for about 5 seconds and then it drops way down to 100-300rpms, idling roughly and cutting out on cold mornings. Engine performance returns to normal behavior when it reaches optimal operating temperature. I'm up in Jersey for the next 6 weeks, and the frigid conditions are not helping the situation. Fuel consumption went from 18mpg to 14mpg. The diagnostic came up with 3 codes:

1. Oxygen Senser transition time (pre-converter, left bank)
2. System too lean, left bank.
3. Engine misfire detected.

I replaced the pre-converter O2 sensor with an AC Delco sensor since all of the symptoms point to that particular part. While the engine runs a little smoother and mileage has improved a little, the surging has gotten worse. In the morning at a stop light, I have to mash the brakes to keep from hitting the car in front of me because the surging is that bad, ranging from 500-1200 rpms. Obviously, I haven't completely fixed the problem.

Should I replace the post-converter sensor on the left bank, or the pre-converter sensor on the right bank, or is it something else? Please don't say it's a bad catalytic converter!
Any suggestions will be greatly appreciated!

p.s. Has any 2000 Silverado owner had a problem with the left upper control arm bushings wearing?

[99ssconv]

1. Oxygen Senser transition time (pre-converter, left bank)
2. System too lean, left bank.
3. Engine misfire detected.

as for oxygen sensor transition time, this code is set because of the misfire, you say misfire detected, which cylinder on the left bank? you need to know which cylinder is misfiring before any further diagnostics. the money you wasted on the oxygen sensor could have been paid for diagnostic time, most shops charge 1 hour labor for check out. i would take it to a dealer before you throw anymore parts on it, i have seen to mamy people guess about whats wrong and end up costing them more than just taking it and getting if fixed, if you know which cylinder is missing then maybe i can help you on this board.

[Bubba14]

timber3
I also have a 4.8 liter silverado except mine is a 1999
If you find out what is causing this problem please post it here.
If I find the fix I will post it here for all to see.
I have the exact same problem.
Mine shows mis fire on cylinders 5 and 8. I have the same codes (mine shows too lean on banks 1 and 2) and rpm's surge same as yours.
After the engine warms up it runs fine.
I have had fuel injecters cleaned (chevy service dept) that's what they said was wrong. IT WASN'T
Took vacuum line off fuel pressure regulator had vacuum and no gas came out. So I changed plugs, plug wires, added dry gas to gas tank, added techron to gas tank,cleaned throttle body with carb throttle body cleaner, changed fuel and air filters, cleaned egr valve, changed idle air control sensor (chevy dealer again) all of this and engine does not run any better.
I have already gone over $500 and no improvement. Most of this money went to the chevy service dept. I need help before I go broke.
Good luck and Thanks Bubba 14

[timber3]

Since the problem is temperature sensitive (when it warms up, the surging goes away), my thinking is that it has to be a component of the open/closed loop system. That's why I thought it might be another bad O2 sensor. Does this make sense?

[juma33]

both of you got vacumn leaks, probably in the head gasket or a gasket somewhere. when the motor warms up the expansion seals the leak to some degree but when its cold you get the full effect - racing motor and lean condition. This is a dealer fix item.

juma

[timber3]

Wow, good thinking. I've got two questions:

Can I detect the vacuum leakage (stethescope)?

Is fluid leakage from the gasket area evident when there's a vacuum leakage?

Thanks for your thoughts.

[juma33]

Can I detect the vacuum leakage (stethescope)? I doubt it but its not totally impossible. It will be near the misfiring cylinder. I would look mainly around the intake gasket.

Is fluid leakage from the gasket area evident when there's a vacuum leakage? depends on where the gasket is broke. could leak oil, water but may not. fluid and oil could just be pulled in and burned like the air that is getting in. look at your oil...if it looks gray, you are getting water. if your using oil, it'll show on the plug for that cylinder. more likely, you'll see nothing.

juma

[Bubba14]

Man I took mine to the chevy service dept and had the intake manifold gasket replaced.
I had sprayed starting fluid around seam of intake manifold and engine rpm's smoothed out when it was surging (when cold).
I could not hear or see the vacuum leak but the starting fluid found it.
Cost was $210

[timber3]

You guys have been very helpful. Let me buy y'all a round of beer! I'm going back home next week and I'll get that gasket replaced. $210 ain't too bad.